1. Field of the Invention
This invention relates to a rod fabricated of non-metallic material for use in supporting the rock formation surrounding an underground passage and, more particularly, to a reinforcing rod fabricated of polymeric material including at one end portion an integral washer element and retainer for receiving torque to rotate the rod when inserted in a bore hole in the rock formation.
2. Description of the Prior Art
In underground operations, such as mining or excavating, one approach to reinforcing the unsupported rock formation is the use of elongated reinforcing rods or bolt members anchored in holes drilled into the rock formation. The bolt member is secured in the bore hole by either engagement of an expansion shell on the end of the bolt with the rock formation or adhesively bonding the bolt by a thermosetting resin injected into the drill hole so that upon curing the bolt member is united with the rock formation. A combination of a mechanical expansion shell and resin bonding is also used in support systems.
A roof plate is retained on the bolt by an enlarged head formed on the bolt or by a nut that is advanced onto the threaded end of the bolt. When an expansion shell is used, the bolt is tensioned with the affect of compressing the rock strata to reinforce the rock strata. When adhesive is used to bond the bolt in the bore hole the resin components are mixed by rotation of the bolt in the bore hole. The mixed resin penetrates into the rock formation to adhesively unite fissures in the rock formation and to firmly hold the bolt in position in the bore hole once the resin cures.
Examples of metallic roof bolts using a combination expansion shell and resin to reinforce a rock formation are disclosed in U.S. Pat. Nos. 4,419,805; 4,413,930; 4,518,292; and 4,516,885. These devices can utilize a metallic roof bolt or reinforcing rod having an enlarged head end forged on the end of the rod that extends from the bore hole. The enlarged head end bears against a metallic roof plate when the bolt is anchored and tensioned to transmit compressive forces to the overlying rock structure. In the alternative, the end portion of the roof bolt is threaded to accommodate a nut. The bearing plate is positioned on the end of the bolt, and then the nut is advanced on the threaded end to hold the bearing plate on the end of the bolt and compressed against the rock structure.
It is also known to reinforce underground rock formations with rods or bolts fabricated of non-metallic material, such as plastic. U.S. Pat. No. 4,369,003 discloses a rock anchor formed of a tubular tensioning element fabricated of glass fiber reinforced synesthetic resin. The tensioning element is anchored within the bore hole by a jacket that is spread by a conical wedge, also fabricated of glass fiber reinforced synthetic resin. The opposite end of the tensioning element which extends from the bore hole includes an externally threaded jacket that is wedged in place on the end of the tensioning element. A metallic anchor plate is positioned on the threaded portion of the tensioning jacket. A clamp nut is threadedly advanced on the end of the jacket to compress the plate against the rock formation. One disadvantage of this type of anchor assembly is the complexity provided by a number of components which must be inventoried and provided for assembly of each anchor. A particular disadvantage is the necessity to thread the end of the plastic anchor to receive a nut without stripping the threads.
U.S. Pat. No. 4,369,003 also discloses that rather than use a fiber glass reinforced spreading jacket, an externally threaded metal spreading jacket may be more efficient to receive a nut to securely retain the anchor plate on the end of the bolt.
It is also known to fabricate high strength non-metallic anchor bolts from materials, such as glass fiber reinforced synesthetic resin. High strength "plastic bolts" are also externally threaded to receive a plastic nut. In many reinforcing applications it is not necessary that the bolt possess the high strength qualities provided by glass fiber reinforced synesthetic resin. Where lesser strength requirements permit polymeric materials having a strength of about 15-25% of glass fiber reinforced bolts can be used.
While it has been suggested by the prior art devices to provide reinforcing roof bolts and rods fabricated of nonmetallic material for use in anchoring rock formations and underground excavations, the known non-metallic rods are expensive to fabricate due to their composition and the number of component parts required. Therefore, there is need in supporting underground rock formations for a non-metallic reinforcing rod or bolt that is economically fabricated and efficiently installed for the particular strength requirements in supporting the rock formation.